1. Field of the Invention
The present invention relates to a gas concentration distribution measuring apparatus which measures a concentration distribution of a gas in a space.
2. Description of the Related Art
An inexpensive and portable gas concentration distribution measuring apparatus which is capable of measuring a concentration distribution of a gas in a space more precisely and faster has been demanded.
Currently, various gas concentration distribution measuring apparatuses, each of which uses a semiconductor type gas detector and has a size that can be held by a single hand and is capable of measuring concentration of a predetermined gas, are known. Among various conventional semiconductor type gas detectors, some take a relatively long time to measure the concentration of a predetermined gas and others can measure the concentration of a predetermined gas in a short time.
It will take a long time to measure the concentration distribution of a predetermined gas in a space by using only one gas concentration distribution measuring apparatus using only one semiconductor type gas detector that takes a relatively long time to measure the concentration of the predetermined gas, and it is highly probable that the concentration distribution of the predetermined gas in the space significantly changes while the concentration distribution of the predetermined gas is measured.
By using a plurality of gas concentration distribution measuring apparatuses each of which uses only one semiconductor type gas detector that takes a relatively long time to measure the concentration of a predetermined gas, the time needed to measure the concentration distribution of the predetermined gas in a space can significantly be reduced. However, it is still probable that the concentration of the predetermined gas in the space changes while they measure the concentration distribution of the predetermined gas. In addition, since the plurality of gas concentration distribution measuring apparatuses is used, preparations for measuring the concentration distribution of the predetermined gas become complicated.
Then, in order to measure the concentration distribution of a plurality of types of gases in a space, a plurality of gas concentration distribution measuring apparatuses each using only one semiconductor type gas detector to measure the concentration of a specific gas in order to measure the concentration distribution of a specific gas in the space are required and thus, still more gas concentration distribution measuring apparatuses are needed in proportion to the number of gases for which concentration measurement is needed.
Even if a gas concentration distribution measuring apparatus which uses a plurality of semiconductor type gas detectors to measure the concentrations of a plurality of types of gases is used, as described above, a plurality of gas concentration distribution measuring apparatuses need to be used to measure the concentration distributions of a plurality of types of gases in a space and thus, a preparation work for measuring the gas concentration distribution still complicated. In addition, if the semiconductor types gas detectors each of which takes a relatively long time to measure the concentration of a predetermined gas are used, it is probable that the concentration distributions of the plurality of types of gases in the space change during measurement.
A semiconductor type gas detector which is capable to measure the concentration of a predetermined gas in a short time utilizes the fact that the value of electric resistance of tin oxide changes with a change in concentration of a predetermined gas. However, such a semiconductor gas detector takes some time to respond to lowering of concentration of the predetermined gas. In addition, when such a semiconductor gas detector is used, it is necessary to heat tin oxide to a high temperature. Therefore, such a semiconductor type gas detector cannot be used for measuring the concentrations of a plurality of types of gases containing a combustible gas. Further, even if such a semiconductor gas detector is used for measuring the concentrations of a plurality of types of gases containing no combustible gas, tin oxide heated to a high temperature causes convection of a gas around the tin oxide and therefore limits a precision of measurement of the concentration distribution of the plurality of types of gases.